Liquid crystals in a TFT-LCD (Liquid Crystal Display) are sandwiched by an array substrate on which there are a TFT and a pixel electrode, and a color filter substrate on which there are a color resin and a common electrode, wherein the liquid crystals inverse when a voltage is applied between the common electrode and the pixel electrode. For a LCD of normally white mode, the less the voltage difference between two sides of liquid crystals is, the larger the transmittance of the liquid crystal molecules are. When a voltage is applied between two sides of the liquid crystal molecules, the liquid crystal molecules rotate, thus making a light provided by a backlight transmitting out through the liquid crystal molecule, wherein the amount of the light transmitted out is determined by rotation angle of the liquid crystal molecules. Due to the property of the liquid crystal molecules itself, if driving with a voltage of only one polarity, the liquid crystal molecules is extremely vulnerable to aging, thus shortening the lifetime of the liquid crystal molecule. Therefore, in order to prevent it from aging, it is necessary to drive the liquid crystal molecules in such a way that voltages of positive polarity and negative polarity are alternately used for driving.
A structural schematic diagram of a TFT in the prior art is as shown in FIG. 1, wherein when the gate line 101 apply a turn-on voltage to the gate 102, the TFT is in an ON state. Data line 103 is connected to the source 104 of the TFT, while the drain 105 of the TFT is connected to the pixel electrode (not shown in FIG. 1). The voltage difference between the pixel electrode and the common electrode set on the color filter substrate drives the liquid crystal molecules to inverse. The common electrode is applied a common electrode voltage Vcom. In FIG. 1, pixel capacitor (CLc) 106 is an equivalent capacitor formed between the common electrode and the pixel electrode. When the TFT is turned on, the pixel capacitor (CLc) 106 is charged through the data line 103. Holding capacitor (Cs) 107 is usually connected in parallel with the pixel capacitor (CLc) 106 to improve its holding property.
After the pixel capacitor (CLc) 106 has been charged, a turn-off voltage is supplied to the gate 102 of the TFT through the gate line 101, the TFT being in an OFF state at this time, and the voltage already charged to the pixel capacitor (CLc) 106 can be maintained until next time the gate is turned on.
A schematic diagram of driving for liquid crystal molecules in the prior art is as shown in FIG. 2. In the Figure, the lateral axis of measured V-T curve 201 for liquid crystal stands for Driving Voltage (V), and the longitudinal axis of the V-T curve stands for Transmittance (T) of the liquid crystal molecules, the V-T curve being determined by the property of the liquid crystal itself. After the V-T curve for liquid crystal is measured, it is needed to determine the dynamic range 202 of driving voltage, and to determine the common electrode voltage 203 based on the dynamic range 202. With respect to the LCD of normally white mode, the lower the voltage difference between the two sides of the liquid crystal is, the larger the transmittance of the liquid crystal molecules is. Thus, the common electrode voltage 203 is chosen as corresponding driving voltage when the transmittance of the liquid crystal is highest, that is, the common electrode voltage 203 may be corresponding abscissa at the maximum of the V-T curve 201. Within the dynamic range 202, the range of the driving voltage higher than the common electrode voltage is defined as positive directional driving voltage range 204, and the range of the driving voltage lower than the common electrode voltage is defined as negative directional driving voltage range 205. The inversion of the liquid crystal molecules is determined by the voltage difference between the positive directional inversion signal voltage and the common electrode voltage when positive directional inversion signal within the positive directional driving voltage range is applied to the source of the TFT; while the inversion of the liquid crystal molecules is determined by the voltage difference between the negative directional inversion signal voltage and the common electrode voltage when negative directional inversion signal within the negative directional driving voltage range is applied to the source of the TFT. In this way, when positive directional driving and negative directional driving, the angles of the liquid crystal rotating toward positive and negative directions are same, making its transmittance to light uniform.
Not only the picture flickering is avoided, but also the liquid crystal is prevented from aging, on the premise that the liquid crystal molecules continuously rotates by setting the common electrode voltage.
A schematic diagram of the TFT array on the array substrate in the prior art is as shown in FIG. 3. Presently, when driving TFT liquid crystal, the inversion manners usually employed are as follows:
(1) Frame Inversion:
That is, the liquid crystal is driven with the voltages of same polarity in one frame of picture, and with reverse polarity of voltage in the next adjacent frame of the picture. A schematic diagram of polarities of voltages between two sides of respective pixel capacitors in TFT array of respective frames when driving liquid crystal to inverse by means of the frame inversion according to the prior art is as shown in FIG. 4.
(2) Row Inversion
That is, in one frame of picture, the pixel capacitors on the same row of gate lines are driven with the voltages of same polarity, and the pixel capacitors on the adjacent row of gate lines are driven with the voltages of reverse polarity. A schematic diagram of polarities of voltages between two sides of respective pixel capacitors in TFT array of respective frames when driving liquid crystal to inverse by means of the row inversion according to the prior art is as shown in FIG. 5.
(3) Column Inversion
That is, in one frame of picture, the pixel capacitors on the same column of gate lines are driven with the voltages of same polarity, and the pixel capacitors on the adjacent column of gate lines are driven with the voltages of reverse polarity. A schematic diagram of polarities of voltages between two sides of respective pixel capacitors in TFT array of respective frames when driving liquid crystal to inverse by means of the column inversion according to the prior art is as shown in FIG. 6.
(4) Point Inversion
That is, the polarities of driving voltage of any adjacent pixel capacitors are different in one frame of picture, and each pixel capacitor is driven with reverse polarity of voltage in the next adjacent frame of the picture with respect to the previous adjacent frame of the picture. A schematic diagram of polarities of voltage between two sides of respective pixel capacitors in TFT array of respective frames when driving liquid crystal to inverse by means of the point inversion according to the prior art is as shown in FIG. 7.
There are problems in driving manners for liquid crystal in the prior art, in that: since one common electrode voltage is employed, there is only one reference voltage when positive directional and negative directional driving for liquid crystal, so that dynamic range of driving voltage is large, as shown in FIG. 2, wherein the driving voltage needs to vary within the range as large as described with reference number 202. However, the magnitude of the range of the driving voltage directly determines the power consumption of liquid crystal driving circuit portion, driving manners for liquid crystal in the prior art may thus result in great power consumption in the course of driving.